EDCA机制下实时业务多跳传输仿真分析

在AdHoc无线自组织多跳网络中,IEEE802.11e协议采用了增强型分布信道接入机制,用于为实时多媒体业务提供有效的QoS保证机制。简单介绍和对比了802.11分布式协调功能和802.11e增强型分布信道接入机制两种信道接入机制,并通过使用网络仿真软件OPNET,模拟了实时的视、音频业务在802.11分布信道接入机制和802.11e增强型分布信道接入机制信道接入机制下在不同网络负载下的性能并进行了仿真分析。     

基于802.11e的无线多跳自适应合作式QoS算法

 为解决Ad hoc网络中转发节点拥塞和低优先级业务增多而影响高优先级业务带宽的问题,提出了一种无线多跳网络服务质量保证框架WMHQ(Wireless Multiple Hop QoS)和自适应合作式信道接入算法QAC-EDCA(QoS guaranteed Adaptive Cooperation EDCA).算法将802.11e的优先级区分机制扩展成了三层优先级机制,通过将业务的服务质量需求映射成时隙利用率进行周期性的监测,并以控制帧捎带的方式在两跳范围内传播竞争窗口调整信息,使得高优先级业务具备剥夺低优先级业务带宽的能力和拥塞节点具有协调获取更多带宽的能力.仿真表明,该算法相对802.11e能更好地保护多跳情况下高优先级业务的服务质量.     

一种采用两级缓冲调度区分业务的帧聚合策略

帧聚合是改善无线MAC(Media Access Control)协议信道利用率,提高频谱效率的有效手段之一。该文针对多业务场景,采用两级缓冲区调度策略,按照不同聚合权重因子对各队列轮询聚合。根据各个队列的包超时紧迫因子动态调整各队列的聚合权重,以满足各QoS等级业务的时延限制。该文还将排队论模型引入到帧聚合策略的性能分析中,建立了系统的数学分析模型,定量分析了主要性能参数与系统负载的关系。通过与IEEE 802.11n标准中定义的两层帧聚合策略比较表明,该文提出的帧聚合策略的性能优于IEEE 802.11n两层帧聚合策略。     

AdHoc多跳网络在EDCA机制下对实时音／视频业务的仿真分析

在AdHoc多跳网络中,IEEE802.11e协议采用了增强型分布信道接入机制（Enhanced Distributed Channel Access,EDCA）,用于为实时多媒体业务提供有效的QOS保证机制。本文简单介绍和对比了802.11分布式协调功能（DCF）和802.11e EDCA两种信道接入机制,并通过使用网络仿真软件OPNET,模拟了实时的视／音频业务在802.11DCF和802.11e EDCA信道接入机制下在不同网络负载下的性能并进行了仿真分析。     

基于IEEE802.11e HCCA的接入控制方案

较传统的IEEE802.11标准的MAC协议,802.11e增强了对QoS的支持力度,主要基于IEEE802.11e的HCCA机制,提出了一套控制接入方案,本方案在全面考虑QoS参数的基础上提出了一个有效的调度算法,从而确保了实时性业务的QoS需要.     

异构无线网络中基于业务转移和接入控制的混合负载均衡

 针对现有异构无线网络负载均衡方法未能综合考虑重载网络业务转移和新业务接入控制的问题,提出了一种混合负载均衡算法.该算法首先根据各小区负载水平和终端移动性,将重载小区的适量业务向重叠覆盖的轻载小区转移;其次通过资源预留和强占优先的接入控制策略,为不同优先级的新到业务提供有差别的服务.仿真结果表明,本文算法在保证系统资源利用率的同时,保障了实时与非实时业务的QoS,并相对于参考算法有效降低了系统阻塞率和业务切换概率.     

IEEE802．11eWLAN中基于HCCA机制的带宽分配算法的研究

随着使用WLAN（无线局域网）接入因特网的日渐普及,IEEE802．11eWLAN中的HCCA（混合控制信道接入）机制由于在处理实时多媒体业务的高效率受到越来越广泛的关注。在WLAN中为达到高带宽利用率和良好的端到端QoS,介绍了一种基于HCCA机制的带宽分配算法,同时对该算法与802．11PCF（点协调功能）两种接入场景下的网络性能进行仿真比较,其结果验证了该算法可以为WLAN提供良好的QoS保证,对在WLAN中传输语音、视频等实时业务具有一定的指导意义。     

IEEE 802.16网络中保障QoS的多用户业务调度算法

基于IEEE 802.16协议,研究了宽带无线接入网中保障Qos的上行多用户多业务资源分配和调度问题.首先,对该问题建立跨层分析模型,即基于TDM-OFDMA物理层的多址接入队列调度模型.随后提出了基于凸优化方法的最小剩余聚合工作负载算法.可以证明,只要到达业务的QOS参数值在该算法的稳定域内,那么它就能渐进地保证业务的QoS要求,同时还能最小化调度系统的剩余聚合工作负载.仿真实验的数值结果进一步证明了本算法的确能够在可接受的复杂度范围内保证4类服务的Qos要求.     

一种基于IEEE802.11EDCF的自适应能量调整算法

简述了IEEE802.11及IEEE802.11e的两种访问控制机制DCF和EDCF,提出了一种基于IEEE802.11 EDCF的自适应能量调整算法,并在NS2上进行了仿真实现.仿真实验结果表明,该算法能够根据分组的优先权水平和节点当前能量值动态调度信道接入,延长了全网的生存期.     

基于M/G/1/K排队模型的IEEE802.11e EDCA性能研究

该文利用二维Markov链分析方法,提出了一种新的IEEE802.11e EDCA网络分析模型,该模型引入了空闲状态和不同接入等级的仲裁帧间隔(AIFS)的使用;利用Markov链状态转移图的Z域信号传递函数推导了MAC层平均服务时间的概率分布;结合M/G/1/K排队模型分析了增强分布式信道接入(EDCA)在非饱和和饱和负载下的性能。经过访真实验结果与数值分析结果的对比,验证了分析模型的准确性。分析结果表明:EDCA接入机制只为不同优先级业务提供QoS区分;不同优先级业务信道接入的不公平性是EDCA接入机制的特点。     

Development of the readout system for waveguide multilayer optical card

Waveguide multilayer optical card （WMOC） is a novel storage device of three-dimensional optical information. An advanced readout system fitting for the WMOC is introduced in this paper. The hardware mainly consists of the light source for reading, WMOC, motorized stages addressing unit, microscope imaging unit, CCD detecting unit and PC controlling ＆ processing unit. The movement of the precision motorized stage is controlled by the computer through Visual Basic （VB） language in software. A control panel is also designed to get the layer address and the page address through which the position of the motorized stages can be changed. The WMOC readout system is easy to manage and the readout result is directly displayed on computer monitor.     

Nanoimprint Lithography -A Next Generation High Volume Lithography Technique

IntroductionNanoimprint Lithography is a well-acknowl-edged low cost, high resolution, large area pattern-ing process. It includes the most promising methods,high-pressure hot embossing lithography (HEL) [2],UV-cured imprinting (UV-NIL) [3] and micro contactprinting (m-CP, MCP) [4]. Curing of the imprintedstructures is either done by subsequent UV-lightexposure in the case of UV-NIL or by cooling downbelow the glass transition temperature of the ther-moplastic material in case of HEL…     

Collinear phase-matching study of terahertz-wave generation via difference frequency mixed in GaAs and Inp

The collinearly phase-matching condition of terahertz-wave generation via difference frequency mixed in GaAs and InP is theoretically studied. In collinear phase-matching, the optimum phase-matching wave hands of these two crystals are calculated. The optimum phase-matching wave bands in GaAs and lnP are 0.95-1.38μm and 0.7-0.96μm respectively. The influence of the wavelength choice of the pump wave on the coherent length in THz-wave tuning is also discussed. The influence of the temperature alteration on the phase-matching and the temperature tuning properties in GaAs crystal are calculated and analyzed. It can serve for the following experiments as a theoretical evidence and a reference as well.     

Effects of the alloy compositions on the phonon-polaritons in ternary mixed crystals

Composition dependence of bulk and surface phonon-polaritons in ternary mixed crystals are studied in the framework of the modified random-element-isodisplacement model and the Bom-Huang approximation. The numerical results for Several Ⅱ - Ⅵ and Ⅲ- Ⅴ compound systems are performed, and the polariton frequencies as functions of the compositions for ternary mixed crystals AlxGa1-xAs, GaPxAS1-x, ZnSxSe1-x, GaAsxSb1-x, GaxIn1-xP, and ZnxCd1-xS as examples are given and discussed. The results show that the dependence of the energies of two branches of bulk phonon-polaritons which have phonon-like characteristics, and surface phonon-polaritons on the compositions of ternary mixed crystals are nonlinear and different from those of the corresponding binary systems.     

Influence of PVK ： NPB hole transporting layer on the characteristics of organic light-emitting devices

A doping system consisting of NPB and PVK is employed as a composite hole transporting layer （CHTL）. By adjusting the component ratio of the doping system, a series of devices with different concentration proportion of PVK ： NPB are constracted. The result shows that doping concentration of NPB enhances the competence of hole transporting ability, and modifies the recombination region of charge as well as affects the surface morphology of doped film. Optimum device with a maximum brightness of 7852 cd/m^2 and a power efficiency of 1.75 lm/W has been obtained by choosing a concentration proportion of PVK ： NPB at 1：3.     

New insert layer structure OLEDs

An insert layer structure organic electroluminescent device（OLED） based on a new luminescent material （Zn（salen）） is fabricated. The configuration of the device is ITO/CuPc/NPD/Zn（salen）/Liq/LiF/A1/CuPc/NPD/Zn（salen）/Liq/LiF/A1. Effective insert electrode layers comprising LiF（1nm）/Al（5 nm） are used as a single semitransparent mirror, and bilayer cathode LiF（1 nm）/A1（100 nm） is used as a reflecting mirror. The two mirrors form a Fabry-Perot microcavity and two emissive units. The maximum brightness and luminous efficiency reach 674 cd/m^2 and 2.652 cd/A, respectively, which are 2.1 and 3.7 times higher than the conventional device, respectively. The superior brightness and luminous efficiency over conventional single-unit devices are attributed to microcavity effect.     

Analysis of error performance on Turbo coded FDPIM

Due to variable symbol length of digital pulse interval modulation（DPIM）, it is difficult to analyze the error performances of Turbo coded DPIM. To solve this problem, a fixed-length digital pulse interval modulation（FDPIM） method is provided. The FDPIM modulation structure is introduced. The packet error rates of uncoded FDPIM are analyzed and compared with that of DPIM. Bit error rates of Turbo coded FDPIM are simulated based on three kinds of analytical models under weak turbulence channel. The results show that packet error rate of uncoded FDPIM is inferior to that of uncoded DPIM. However, FDPIM is easy to be implemented and easy to be combined, with Turbo code for soft-decision because of its fixed length. Besides, the introduction of Turbo code in this modulation can decrease the average power about 10 dBm, which means that it can improve the error performance of the system effectively.     

A method for calculating the center position of collimated light

It is a key problem to accurately calculate beam spots＇ center of measuring the warp by using a collimated laser. A new method, named double geometrical center method （DGCM）, is put forward for the first time. In this method, a plane wave perpendicularly irradiates an aperture stop, and a charge couple device （CCD） is employed to receive the diffraction-beam spots, then the geometrical centers of the fast and the second diffraction-beam spots are calculated respectively, and their mean value is regarded as the center of datum beam. In face of such adverse instances as laser intension distributing defectively, part of the image being saturated, this method can still work well. What＇s more, this method can detect whether an unacceptable error exits in the courses of image receiving, processing and calculating. The experimental results indicate the precision of this method is high.     

Cost-effective test solutions for smart card and other integrated flash applications

From its emergence in the late 1980s as a lower cost alternative to early EEPROM technologies, flash memory has evolved to higher densities and speedsand rapidly growing acceptance in mobile applications.In the process, flash memory devices have placed increased test requirements on manufacturers. Today, as flash device test grows in importance in China, manufacturers face growing pressure for reduced cost-oftest, increased throughput and greater return on investment for test equipment. At the same time, the move to integrated flash packages for contactless smart card applications adds a significant further challenge to manufacturers seeking rapid, low-cost test.     

An improved parallel thinning algorithm with two subiterations

The parallel thinning algorithm with two subiterations is improved in this paper. By analyzing the notions of connected components and passes, a conclusion is drawn that the number of passes and the number of eight-connected components are equal. Then the expression of the number of eight-connected components is obtained which replaces the old one in the algorithm. And a reserving condition is proposed by experiments, which alleviates the excess deletion where a diagonal line and a beeline intersect. The experimental results demonstrate that the thinned curve is almost located in the middle of the original curve connectivelv with single pixel width and the processing speed is high.